Testing carbonates in weak acids

Calcite freely produces bubbles when placed in household vinegar. I usually place a tiny fragment of the mineral to be tested in a small shot glass and look for bubbles on the surface of the sample under low power microscope.

My question is will other carbonates also test positive in household vinegar? Specifically interested in distinguishing calcite from rhodochrosite.

In vinegar, aragonite will bubble as much as calcite. Dolomite will bubble but very slowly. I haven't seen any reaction with rhodochrosite or siderite. Siderite was the most resistant of the group, in my limited experience - You need a strong mineral acid, and even then you have to heat it. Even with vinegar, heating makes a big difference to speed of reaction.

(At this point on Mindat, somebody usually steps into the discussion to remind us how dangerous this is and say we're all gonna die, so I'd like to state up front that I use only tiny grains of mineral, in a few drops of acid, and point the test tube away from my eyes while warming over the flame, so death is far more likely to come via my skis, bike or french fries than from my chemistry set.)

This is very dangerous and you're all going to die!!!!!! Sorry, I couldn't resist....

I don't ever remember rhodochrosite bubbling in vinegar, but in heated HCL it will bubble vigorously. Same with dolomite, magnesite, and a fresh surface of siderite. If it's what I'm thinking you're trying to ID George (UP specimens?), the rhodo will have a very slight pink tint to it where the calcite is white, in most cases of course.

A standard field geologist's test is to try applying dilute acid to a carbonate before and after powdering. Calcite will fizz without the need to powder the sample. Dolomite will fizz but only after the rock sample is powdered, usually by vigourously scratching the surface of the mineral with a tungsten carbide scriber. There are a whole series of simple mineral tests given in Donald Peck's book, Mineral Identification. You can get this from the Mineralogical Record website. A very useful book for anyone interested in identifying their own specimens. Both amateurs and professionals use it.

It is important to remember that the rate of a reaction is related to the size of the particles, the temperature, the strength of the acid (degree of ionization), and the concentration (dilution). So one has to be careful in generalizing about the different species of carbonates and how much or how little they bubble with acid. For careful work, I prefer using a small amount of finely powdered mineral in the well of a depression microscope slide. The acid can be placed above the well on the slide until it is under the microscope and then drawn into the well with a probe. If heating is required, the slide can be heated by passing it through an alcohol lamp flame or setting it on a lamp bulb. I have not tried to quantify the difference in effervescence among mineral species, except for calcite and dolomite. The detection of iron or manganese is extremely easy and can be done on the drop or two of solution remaining in the well.

Another thing, vinegar is easily available, but its concentration is not always the same. In most of the US it is 5%, but in some states it is higher. I think in the UK it may be 20%. All this affects the rate of reaction.

Please, enter the code that you see below in the input field.
This is for blocking bots that try to post this form automatically. If the code is hard to read, then just try to guess it right.
If you enter the wrong code, a new image is created and you get
another chance to enter it right.